29 December 2016 - A PARTIAL LUNAR ECLIPSE


G'day folks,

A lunar eclipse occurs when the Moon passes directly behind the Earth into its umbra (shadow). This can occur only when the sun, Earth and moon are aligned (in "syzygy") exactly, or very closely so, with the Earth in the middle. Hence, a lunar eclipse can occur only the night of a full moon.

A partial lunar eclipse happens when the Earth moves between the Sun and the Moon, but they are not precisely aligned. Only part of the Moon's visible surface moves into the Earth's shadow.

What Causes a Partial Lunar Eclipse?

A partial lunar eclipse occurs when the Earth moves between the Sun and Moon but the 3 celestial bodies do not form a perfectly straight line in space. When that happens, a small part of the Moon's surface is covered by the darkest, central part of the Earth's shadow, called the umbra. The rest of the Moon is covered by the outer part of the Earth's shadow called the penumbra.

 Conditions for a Partial Lunar Eclipse


For a partial lunar eclipse to occur, 2 celestial events must happen at the same time:
  • The Moon should be a full Moon.
  • The Sun, Earth and Moon must be aligned in almost a straight line.


 Not Every Full Moon Night


Partial lunar eclipses do not happen every full Moon night because of the inclination of the Moon's orbital plane. The Moon's orbital path around the Earth is inclined at an angle of 5° to the Earth's orbital plane (ecliptic) around the Sun. The points where the 2 orbital planes meet are called lunar nodes.

Eclipses can only happen near the lunar nodes. Lunar eclipses occur when a full Moon happens near a lunar node, and solar eclipses take place when a new Moon occurs near a lunar node.

 How to See?

Partial lunar eclipses can be seen across the night-side of the Earth. No special equipment is needed to see a partial lunar eclipse. All you need is the exact date and time for the next eclipse to be seen from where you are, the weather forecast, some warm clothes and a chair to keep you comfortable while you watch the eclipse unfold.

Clancy's comment: There ya go. I knew you were dying to know that.
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